Editing the weather observations

Original oW1 observations (red dots) and as revised using the edited ship histories (smaller yellow dots). Some new observations have been added (ships for which we now have good positions), a few errors in the original observation set have been removed, and much valuable new detail has been added.

However, we said at the time that those were preliminary data. They were useful as they were, but we hoped to improve them further in the future. In particular we struggled to get good position information from every logbook page: Generally, when they reported their latitude and longitude (’32 27 03 N’, ’24 78 08 W’) we could locate them successfully (though there are difficulties), but often the logs give their location as the name of a port or place, and tracking that down can be hard.

When we made the preliminary set of climate data we did all the data processing (to turn the log transcriptions into climate records) in software. This is fast, but not powerful enough to deal correctly with the difficult positions. It got us what we most needed (as much data as possible, now) but a substantial fraction of our 1.6 million observations were left with positions that were missing, approximate, and, occasionally, just wrong. These issues did not damage climate products using the observations, but they did restrict them. Effectively, many of our observations were not good enough to use. What we really needed was a careful, expert examination of the record for each ship, teasing out the precise route of each ship from the limited, idiosyncratic, and occasionally just wrong, information in the log. This would require two things, a group of expert analysts, and time for them to work.

One of the glories of oldWeather is the expertise and dedication of the project community, and the ship history editors, in particular, have been working through the log transcriptions, using their expertise to make edited histories, and maps, of their travels. They have not had enough quite time to finish the task – not every ship has yet been edited – but most are done, and once again we need the data now. So I have gone through the edited histories and used their position records to improve the weather data records.

This has improved our weather records a lot (see the video above). Some ships with log details that defeated the software the first time around now have good positions and can be used for the first time. More have details improved and some errors fixed. A particularly noticeable improvement are the gunboats on rivers in China, which now show movement along the Yangtze in good detail. We still have 1.6 million records, but about 500,000 of them have received a big upgrade in their quality, and this will feed through to substantial improvements in the climate products we derive from them.

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2 responses to “Editing the weather observations”

Don’t forget the positions themselves can be in error, both from errors in taking the star sights and also from errors in dead reckoning if it had been cloudy. I remember tales when I was taught navigation that when asked where the ship was the navigator put his fist on the chart and said here. Not quite as silly as it seems as when large scale charts are used a long way from land the uncertanties are normally larger and matter less. The danger is when you close land and need a small scale chart – the fist then covers a smaller area of sea showing the uncertanties are less.